The present invention relates to a new and improved reticle assembly, system, and method for use in the manufacture of semiconductor devices. The present invention more particularly relates to a reticle assembly, system, and method for exposing each of a plurality of device dies of a semiconductor wafer to a pattern of radiation on a site-by-site exposure basis using a reticle having a plurality of sites wherein each site is for a different device, a different level of the same device and/or a cluster of the same level of a device.
Processes for manufacturing semiconductor devices, such as discrete devices and integrated circuits, hereinafter referred to generally as devices, have become highly developed in the art. In general, the devices are formed in semiconductor wafers, which can be two to twelve inches in diameter, by diffusing various impurities into selected regions of the wafers to form the devices and by depositing metal onto the wafers in discrete regions to provide circuit interconnects. In such processes, the wafer is subdivided into a plurality of small discrete areas, referred to as dies, with each die corresponding to one of the devices. The wafers are processed in tact until the dies have been finally processed, at which point, the wafer is scribed or otherwise physically cut into the aforementioned dies. The dies are thereafter mounted into suitable packages having external pins which are connected internally to die bonding pads. Thereafter, the packages are encapsulated and ready for use.
To define the discrete regions of the dies wherein impurities are diffused or whereon metal is to be deposited, photolithographic techniques are generally employed. In such a process, a radiation sensitive material, such as a photoresist which is sensitive to a given source of irradiation, is coated over the wafers. The wafers are then exposed to the given irradiation, such as ultraviolet light irradiation, electron beam irradiation, or x-ray irradiation through a mask or reticle which has a pattern of opaque and transparent areas so that the radiation source impinges upon the photoresist in only those areas defined by the transparent areas. After exposure, the wafers are subjected to a suitable developer which removes the photoresist in those areas which were exposed or not exposed, depending upon whether a positive or negative photoresist was used. As a result, discrete areas of the wafers are left covered by photoresist and the other areas are rendered uncovered to ultimately permit diffusion of impurities into the uncovered areas or deposition of metal over the uncovered areas.
One process for exposing the wafers through a reticle to a source of radiation, such as ultraviolet light, for example, is a projection and step and repeat process wherein the reticle defines the radiation pattern for each die. Also, optics may be used so that the reticles can be physically larger in dimension than the die size. The optics reduce the reticle dimension to the die size and forms the reticle pattern on the wafers. Hence, because the reticles can be larger than the die size, very small feature sizes, down to less than one micron, can be obtained. Because the ultimate pattern image has the dimensions of the die, the wafer is generally incrementally moved relative to the reticle on a step and repeat basis so that the entire wafer is exposed to the reticle pattern on a site-by-site exposure basis.
Usually, many such exposure steps are required in manufacturing semiconductor devices. This results because the devices include many different elements which are formed in levels within the semiconductor wafers. Each such level requires a separate exposure, and each such exposure therefore requires a respective different reticle. It is not unusual for a device to require twelve different exposures and thus twelve different reticles.
Because high precision is required in making reticles, the cost of making reticles is quite high. This high cost can be tolerated in high volume, mass production environments, but can be exorbitant for low volume production environments, such as in making custom devices or making devices during device design and development